1. Field of the Invention The present invention concerns an optical head in hybrid technology, namely an optoelectronic module that enables the emission and reception of light signals, conveyed by a single optic fiber, the module being made by means of hybrid technology, so that it can be directly fitted into a hybrid circuit.
2. Description of the Prior Art
In the single-fiber bidirectional optic link, the single optic fiber transmits the light, emitted by a laser diode placed at a first end of the fiber and received by a photodiode placed at a second end of the fiber, in a first direction that shall be called a forward direction. In the other direction, which shall be called the return direction, the light emitted by a second laser, placed at the second end of the fiber, is received by a second photodiode placed at the first end of the fiber. Therefore, at each end of the optic fiber, there is a laser diode and a photodiode, both of which should be optically linked to that end of the optic fiber which is in their vicinity.
FIG. 1 shows the block diagram of a bidirectional optic fiber termination: the single optic fiber 1 transmits the light received by the photodiode 3 in one direction The respective dimensions of the optic fiber 1 and of the two semiconductors 2 and 3 make it necessary to multiplex the light beam by a duplexer 4, connected to the laser by a fiber section 5 and to the photodiode by a fiber section 6. The blocks 7 and 8 represent, respectively, the electronic circuits for emission and reception of the signals.
The known ways of carrying out this duplexing or optic coupling are fairly bulky as a rule: the couplers are formed by a package, the faces of which support optic connectors. There is at least one connector for the optic fiber, one connector for the laser in its micropackage and one connector for the photodiode in its micropackage. Within the package of the coupler, simple means couple the laser to the optic fiber and the photodiode to the optic fiber. The main drawback of these couplers, which are moreover simple elements, is the amount of space they occupy. Besides, owing to the very small dimensions (50-100 .mu.m) of the optic fibers used in bidirectional systems, the couplers require high machining precision at each connection by connectors.
FIG. 2 shows a simplified sectional view of a prior art duplexer such as this. A package 4 supports three optic connectors 9, 10 and 11. The optic fiber 1 is fixed into the connector 9, and the signals that it conveys are relayed towards the connectors 10 and 11 by means of two fiber sections 13 and 14, coupled in the region 15. The fiber sections 5 and 6 of FIG. 1 are connected to the connectors 10 and 11. This duplexer, which besides is highly efficient, is not capable, in itself, of being fitted into a hybrid circuit, and requires three optic connectors which are known to be difficult to use.
In order to do away with the need for optic connectors, the Applicant has developed and perfected an optic head shown in FIG. 3. This head uses a TO39 type transistor package, available in the market, the cover 16 of which is provided, by construction, with a lens 17. The chips of a laser 2 and of a photodiode 3 are fixed to the base 18 of the transistor package. The light emitted by the laser 2 is focused towards the optic fiber 1 by a spherical lens 19 and by the lens 17 of the package cover. In the emission mode, the semi-transparent mirror 20 does not come into play. In reception, the light transmitted by the optic fiber 1 is reflected by the mirrors 20 and 21 towards the photodiode 3. The assembly is described in detail in the French patent application No. 85 07147 filed on 10th May 1985.
This duplexer is easy and economical to make, but it is three-dimensional: if the base 18 is fixed to a substrate conventionally, the optic fiber 1 is perpendicular to the substrate and, hence, is in an inconvenient position where it is subjected to a risk of breakage. For the optic fiber to be in a plane parallel to that of the substrate, the TO39 package would have to be fixed in a cradle, its axis of symmetry being parallel to the substrate. These techniques are not homogeneous with the technology of hybrid circuits.